1. Field of the Invention
This invention relates to a support element, an upright support formed of such elements and a support structure further including cranks or shelves supported by such upright supports, for supporting articles during kiln firing.
2. Description of the Prior Art
During the firing of plates and similar articles, the articles have previously been supported by cranks made as unitary structures in refractory material and usually having three generally horizontal legs extending angularly away from the centre of the crank to respective vertically depending stackable feet. The cranks, together with the plates or other articles supported thereon were then stacked in columns on a refractory base and introduced into the kiln for firing of the ware.
Firing of larger articles such as cups, bowls and the like has conventionally achieved by placing the articles on shelves or "bats" supported on upright support pillars or walls. Commonly, some shelves at least are fixed by being trapped between adjacent elements of the support pillars or walls, although intermediate shelves may also be slid onto projecting shelf supports.
Using either of the above described prior arrangements, serious problems are now being encountered because of the introduction of fast firing kilns which will fire ware in typically one hour or less, instead of several hours as was the case with older types of kiln. The introduction of such fast firing kilns is becoming widespread, owing to the rising cost of fuel and to the relative compactness of fast firing kilns.
The supporting structure is now subjected to rapid heating and cooling, which gives rise to relatively high rates of thermal expansion and contraction. The types of support structure outlined above are vulnerable to damage by cracking as a result of the high stresses to which they are subjected during fast firing. This is particularly so because of the way in which the crank feet are effectively clamped in stacks under the load of the supports plus the ware or, in the case of shelf arrangements, the way in which the shelves are clamped rigidly at their edges between the upright support pillars. This rigid clamping under load prevents adequate release of thermal stress.
Further, the large bulk of material present at the stacked crank feet or at the supports of a shelf-type support structure gives rise to thermal inertia on heating and cooling. For example, on heating, the kiln gasses circulating around the surfaces of these relatively massive parts of the structure will heat the surfaces very rapidly while the relatively deep lying inner regions are still cool, causing local stresses in the material. Heat is stored in large quantities in the thick bulky parts of the structure when they have been heated up, which wastes otherwise useful heat, and further gives rise to risk of cracking as the structure cools.